Thank you! That site was extremely helpful. I am now working on plugging all the correct values in to get a "normal" sounding answer. Thank you for helping me.

Jun 12th 2009, 05:27 PM

matheagle

Quote:

Originally Posted by drichie

hint:

If and are independent normal random variables, then:

NOTE that the two populations variances are equal .
In this case you are supposed to pool the sample variances.

Jun 14th 2009, 09:27 AM

madgab

(seems high)

This answer doesn't seem quite right.

Then how do I do the confidence interval using the 90% CI, 1.645?

I was going to just do
but neither of my answers seemed to make any sense.

Jun 16th 2009, 07:44 AM

madgab

Thank you for all the help on this problem. I do not understand why the population variances are equal, or how you figure that. I have been going through different books and thought I could just use the equation that uses just the sample means and variances with the t value from the table. I'm sure I'm wrong, I just can't figure out how to tell that the pop variances are equal. Thanks

Jun 16th 2009, 07:56 AM

matheagle

Who ever gave you this problem stated that the variance of X and the variance of Y was ,
otherwise they would have said

and .

IN this case you need to pool the variances.
And it's a t percentile and not a z, as I stated a week ago.